[fix] remove image decoding

Removed the code for image decoding. You should decode image manually using the following code.
```python
from io import BytesIO
from PIL import Image

Image.open(BytesIO(image_bytes))
```

Example:
```python
import datasets
ds = datasets.load_dataset("jxu124/OpenX-Embodiment", "fractal20220817_data", streaming=True, split='train', trust_remote_code=True) # IterDataset
for d in ds:
break
image_bytes = d['data.pickle']['steps'][0]['observation']['image']

from io import BytesIO
from PIL import Image
image_pil = Image.open(BytesIO(image_bytes))
```

OpenX-Embodiment.py

@@ -15,20 +15,15 @@ except ImportError:
 
 
 def load_webdataset(filepath):
-    def decode_image(data):
+    def decode_data(data):
         if isinstance(data, dict):
-            data = {k: decode_image(v) for k, v in data.items()}
+            data = {k: decode_data(v) for k, v in data.items()}
         elif isinstance(data, tuple) or isinstance(data, list):
-            data = [decode_image(v) for v in data]
+            data = [decode_data(v) for v in data]
         elif isinstance(data, np.ndarray):  # wds to datasets
             data = data.tolist()
-        elif isinstance(data, bytes):
-            if len(data) > 1024:
-                data = PILImage.open(BytesIO(data))
-            else:
-                data = data.decode()
         return data
-    return wds.WebDataset(filepath).decode().map(decode_image)
+    return wds.WebDataset(filepath).decode().map(decode_data)
 
 
 _OPENX_DATASETS = {